When people think of prostitution and the sex trade in Central Massachusetts, the usual image is of women flagging down cars in Worcester's Main South.

But that's only part of the story. These days, much of the illicit business has been occurring in suburbia, where local police are finding “massage” parlors and prostitutes setting up shop.

Police officials in communities outside the city say the security and low crime rates in suburban towns have, ironically, become the draw for the illegal activities.

“The interesting thing is one of the questions we've asked has been why Northboro?” Northboro Police Chief Mark K. Leahy said. “We had one girl, she was from the Fall River/Attleboro area, and her response was, 'I feel very safe here.' Now that's not exactly the aspect of crime prevention that we've been going for.”

And it's not just at lower-cost hotels such as the Motel 6 in Northboro where prostitutes have been a recurring problem, said Westboro Police Chief Alan Gordon. He said the women have even booked rooms at pricier hotels in his town.

“They do feel safe. They have a less of a chance of being ripped off or hurt,” Chief Gordon said. “There is a higher clientele here too. There are a lot of white-collar jobs around here. It is an area they can certainly make a lot more money.”

Detectives mine websites such as Craigslist and Backpage for the illicit offers. A couple of years ago a phalanx of attorneys general across the country demanded that Craigslist shut down its adult services section, and the company eventually agreed to do so.

But for every Craigslist a new company is ready to fill the void. Authorities say Backpage took over the niche left by Craigslist.

Village Voice Media, and its owners Jim Larkin and Michael Lacey, retain ownership of the website. Village Voice Media sold its newspapers to another group but the website was not part of the deal.

Backpage.com lists escorts and other fetish services in the advertisement section, nestled near sections for car sales. A search for Westboro nets several advertisements for escorts, some with pictures.

“Sexxy hot girlfriend for hire,” one ad reads. “Early morning special for a sunny day,” another ad says.

Some even come with disclaimers saying that any money exchanged is for companionship. Also some disclaimers say, “By contacting me you agree to these terms and hereby agree that you are not part of any law enforcement agency using this advertisement for entrapment or for arrest.”

Easy access to highways is another reason Northboro, Westboro and Auburn have become a draw for prostitutes. Northboro and Westboro are tucked right around Routes 20 and 9, with Interstate 495 nearby.

“We've gone up and confronted some people,” Chief Gordon said. “They leave very soon after they are aware we are aware of it.”

Many of the prostitutes come from the Providence area, others from Hartford, authorities said. The prostitutes even use websites to find cheap room rates.

Auburn Police Chief Andrew J. Sluckis, noting that Routes 12 and 20 are in his town along with Interstates 290, 395 and the Massachusetts Turnpike, said “escorts” have “told us that is easy for them to get to because of the roadways that go through here.”

His detectives have done stings and have flat-out asked prostitutes to leave town. His department also keeps an open line of communication with the motel owners.

“We have worked and do continue to work with the hotel management and the hotel employees,” Chief Sluckis said.

Paul J. Sacco, president and CEO of the Massachusetts Lodging Association, said having a good relationship with law enforcement helps motel and hotel owners.

“If the room is being used in an illicit way, we always encourage owners to call police,” he said.

Innkeepers can take action if someone in their establishment hinders the safety of guests and employees, Mr. Sacco said. He suggests staff be aware of suspicious activity and report anything suspicious while cleaning rooms.

“We do suggest, say the next day if the housekeeper is making up the room and sees something that might be questionable, that they inform their supervisor accordingly,” he said.

It is not just prostitution that police in Central Massachusetts are dealing with. Massage parlors that authorities allege offered sexual services have been shut down in Oxford, Millbury, Hopedale and Worcester.

Oxford police found information on an alleged massage parlor doubling as a prostitution house on Backpage.com as well.

“The whole thing, it carries over not only to motels, but massage parlors,” Chief Sluckis said. “We've shut down two different massage parlors in town.”

The Worcester district attorney's office has taken notice as well. Besides the illegal activity involved in the sex trade, some of these cases involve victims many people don't think about.

“We take these cases very seriously,” District Attorney Joseph D. Early Jr. said. “It's not just that a massage parlor has employees performing sex acts. These are young women from other countries who come here expecting an education and a good job. Instead they are forced into being sex slaves.”

Those taking advantage of these women prey on their dreams of escaping poverty. Violent assaults and drug dealing are sometimes associated with these illegal activities, Mr. Early said.

“Their dreams and ambitions are used against them to get them here and once here they have no choice but to participate or face the risk of being assaulted, beaten or even killed,” he said. “This isn't the movie 'Pretty Woman,' and it isn't a choice.”